Electric heater



I May 2, 1944. L, M. DALY 2,347,993

ELECTRIC HEATER Filed Jan. 11, 1943 Inventov: Loretta M. Dalg,

H 21- Attorney.

Patented May 2, 1944 ELECTRIC HEATER Loretta M. Daly, Pittsfleld, Mass.,assignor to General Electric Company, a corporation of New YorkApplication January 11, 1943, Serial No. 471,940

3 Claims. '(Cl. 201-67) More particularly, this invention relates to Isheath wire heating units wherein the resistance conductor is embeddedin a compacted mass of granular insulating material enclosed in ametallic containing sheath. To the ends of the resistance conductor aresecured terminals which project from the sheath. In the construction ofthe heating unit, the resistance conductor with the terminals attachedis first temporarily secured centrally in the sheath, for example, bysecuring the outer ends of the terminals; and then the sheath is filledwith granular insulating material, and its length increased and itsdiameter reduced to compact the insulating material by swaging, rollingor drawing the sheath. Also, electrically insulating centering membershave been provided as additional means for centering the terminals inthe sheath during the construction of the unit in order to preventdisplacement of the terminals and resistance conductor. These centeringmembers are in the form of washers threaded on the terminals; and incertain cases they have been held in their proper positions on theterminals by flattening the terminals or upsetting them in order to formoutwardly extending projections on opposite sides of the washers.

Once the terminals have been flattened to upset them there is no way ofreplacing a washer in case one becomes broken or seriously damaged.Moreover, the upsetting and flattening of the terminals weaken them attimes to such an extent that they pull apart when the length of thesheath is increased and its diameter reduced, thereby causing opencircuits. In addition, the flattening and upsetting operations workharden the terminals, and it is impossible to anneal them since theinsulating washers are on the terminals and would be destroyed in theprocess.

This invention contemplates the provision of improved means-for holdingthe washers on the terminalsjkancl hi one form thereof this means is inthe form of resilint clips which resiliently engage the terminal onopposite sides of the washer so'as to hold it in place. The clips in oneembodiment are in theiorm of broken coils or rings metaLwhich haveresiliency to grip the terminal with sufficient force to remain in placewhile the heater unit is being made.

For a more complete understanding of this invention, reference should behad to the accompanying drawing in which Fig. 1 is a fragmentaryelevation of a sheathed heating unit at one stage in the process ofmaking the heating unit; Fig. 2 is a sectional view taken through theline 2-2 of 1 and looking in the direction of the arrows; Fig. 3 is afragmentary elevation illustrating the e ctric heating unit after it hasbeen made; and g. 4 is a perspective view of a terminal of the heater ofFigs. 1-3, and illustrating supporting means therefor arranged inaccordance with this invention.

Referring to the drawing, this invention has been shown in one form asapplied to an electric heating unit I!) having a helical or sinuousresistance conductor Ii extending centrally of a metallic sheath 12. Theheating element H in the finished heating unit (Fig. 3) is embedded in acompacted mass of powdered, heat-refractory, electrically-insulatingmaterial l3, such as powdered magnesium oxide. A pair of terminals l4and I5 are secured to the opposite ends of the resistance element il.These terminals also are embedded in the compacted mass of insulatinmaterial i3, and they have their ends projecting from the sheath, asshown in Fig. 3. The resistance conductor may be secured to theterminals in any suitable way, but preferably it will be threaded onthem, as shown.

In making the heating unit shown in Fig. 3,

the opposite ends of the resistance conductor ll are threaded on theends of the terminals, and then the assembly of resistance conductor andterminals is inserted into the sheath. Prior to the assembly of theterminal H with the resistance conductor, a solid washer I6 is threadedon it, the washer being prevented from moving outwardly from theterminal by means of a. flattened portion I! provided on the end of theterminal. This washer I6 seats in a recess !8 provided in the end of thesheath, as shown in Fig. 1. The sheath is peened over as indicated bythe numeral Is in order to secure the washer in its position in therecess 48. It will be understood that the opposite terminal-theright-hand one as viewed in the drawing-will also be provided with aflattened section similar to the section ll, but in this case it will beprovided with an aperture and through this aperture there will beprovided a pin which is received in a recess in the sheath similar torecess H3 in order to hold the outer end of this terminal in place. Theinsulating material I3 is loaded through this right-hand end of thesheath with the sheath in an upright position, the material beingretained by the solid washer l5 at the bottom.

After the sheath has been loaded it is elongated so as to reduce itsdiameter to thereby highly compact the insulating material I3. This maybe accomplished by swaging or rolling or drawing the sheath through asuitable die. Following this, the ends of the sheath are cut away so asto leave the outer ends of the terminals projecting from it.

In order to support the inner ends of the terminals l4 and I5 during theloading and swaging operations so as to prevent displacement of theterminals from the center of the sheath, an electrically insulatingwasher 20 is threaded on each terminal at a point remote from the fixedouter end, as shown in Figs. 1 and 4. The insulating washer has anon-circular shape-that shown in the drawing being substantially square.By reason of this arrangement the corner sections of the washer coactwith the sheath to prevent displacement of the washer crosswise of thesheath, and hence prevent displacement of the terminal and theresistance conductor connected with it from the center line of thesheath. Also, because of this arrangement spaces 2| are left between tieinsulating washer and the sheath through which the insulating materialmay flow past the washer.

The insulating washer 20 is held in its proper position with relation tothe terminal by means of a pair of resil ent cliplike members 22positioned on opposite sides of the washer, as clearly shown in thedrawing. Each of these members is in the form of a broken ring or coilwhich has a diameter somewhat smaller than the diameter of the terminalso that when it is threaded on the-terminal it is expanded somewhat.Furthermore, the clips are formed of a resilient, springy material sothat when they are inserted on the terminal and expanded they grip theterminal with sufficient force to prevent slipping lengthwise of theterminal, whereby they hold the wash- ,ers firmly in place while thesheath is being loaded and while it is being compacted.

While the insulating washers are formed of a material which is rigid tohold the terminals central during the loading operation, it is readilydestructible when subjected to the pressure of the sheath on it duringthe swaging or drawing or rolling operation. And while any suitableelectrically insulating material having these characteristics may beused, I prefer to form the washers of lava.

It will be understood, therefore, that in making the heater aspreviously described, the insulating washers 20 will be threaded uponthe terminals and secured by their clip 22 before the termials aresecured to the resistance conductor I I. Then the sheath may be loadedand swaged as previously described. During the swaging operation, theinsulators are destroyed and in the finished heater perform no usefulfunction.

It will be observed that I have provided means for supporting theterminals which does not necessitate flattening sections of theterminals or upsetting them.in any way to provide ears. But on thecontrary, I have provided a relatively simple, inexpensive, andefficient means for holding the washers in place. If for any reason itshould vbe desired to replace a washer it is merely necthat I do notwish to be limited thereto since many modifications may be made, and I,therefore, contemplate by the appended claims to cover any suchmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an electric heating unit comprising a sheath, compacted granularinsulating material within said sheath, a resistance conductor embeddedin and supported in said insulating mate rial, and a terminal for saidresistance conductor also embedded in and supported by said insulatingmaterial, means for supporting said terminal within said sheath whilesaid insulating material is inserted in the sheath and compactedcomprising an insulating spacing member threaded on said terminal, andresilient members on opposite sides of said spacing member frictionallyengaging said terminal to prevent displacement of said member withreference to said terminal.

2. In an electric heating unit comprising a sheath, compacted granularinsulating material with-in said sheath, a resistance conductor embeddedin and supported in said insulating material, and a terminal for saidresistance'conductor also embedded in and supported by said insulatingmaterial, means for supporting said terminal within said sheath whilesaid insulating material is inserted in the sheath and compactedcomprising an insulating spacing member threaded on said terminal, andresilient clips encircling said terminal on opposite sides of saidspacing member engaging said terminal with sufficient force to preventdisplacement of said spacing member, but yielding to permit withdrawalthere of from said terminal.

3. Supporting means for the terminal of a sheathed heater wherein theterminal is of rodlike form comprising an electrically insulatingcentering member threaded on said terminal, and a pair ofbroken-ring-like resilient clips threaded on said terminal on oppositesides of said member resiliently engaging said terminal to preventdisplacement of said member lengthwise of said terminal,

LORETTA M. DALY. I

